Broadband waveguide slot radiator with mutually coupled slots of different perimeters and orientation



BROADBAND WAVEIEEUIDE SLOT RADIATOR WITH MUTUALLY COUPLED SLOTS O E DIFFERENT FE'RIMETERS AND ORIENTATION Filed. March 28', 11965 2 Sheets-Sheet 1 Ara/game QMN. 24-

May 11, 1965 J. s. AJIOKA 3,133,511

BROADBAND WAVEGUIDE SLOT RADIATOR WITH MUTUALLY COUPLED SLOTS OF DIFFERENT PERIMETERS AND ORIENTATION Afraewzx United States Patent Cfiice 3,l83,5ll Patented May ll, 1965 Delaware Filed Mar. 28, 1963, Ser. No. 268,613 8 Claims; (Cl. 343-771) The present invention relates to waveguide radiating elements and, more particularly, to a broadband waveguide slot radiating element which includes one or more driven slot radiators and one or more parasitic (undriven) slot radiators disposed in close proximity to each other in the narrow wall of increased-height rectangular waveguide.

Transverse slots in the narrow wall of rectangular waveguide do not normally radiate when electromagnetic energy is propagated through the waveguide in the dominant mode. The reason for this is that the current flow within the waveguide is parallel to the slot. One way of obtaining radiation from a transverse slot in the narrow wall of a rectangular waveguide is to incline the slot from the transverse position so that at least a component of the current is transverse to the narrow dimension of the slot. In such an arrangement, the polarization of the electric lield of the resulting radiation from the slot is transverse to the slot and nominally parallel to the longitudinal axis of the waveguide.

As is generally known, the perimeter of a slot is approximately equal to the wavelength at which the slot resonates. It is the present practice to wrap slots aroun the narrow wall of the waveguide when it is desired to achieve resonance at a frequency corresponding to a longer perimeter than can be accommodated by the narrow wall thereof. When using slots of this type in a two-dimensional array, it becomes impossible to use adjoining waveguide with a common broad wall thereby eliminating the possibility of having a smooth ground plane. This also makes it necessary to employ shielding between adjacent waveguide-to prevent radiation towards the backside of the array and, in addition, complicates pressurization because of the lack of equalizing pressures on the broad wall of the waveguide.

It is therefore an object of the present invention to provide an improved waveguide radiating element.

Another object of the present invention is to provide waveguide radiating elements that when used in a twodimensional array result in an antenna that is less cxpensive to fabricate and that is of lighter weight.

Still another object of the invention is to provide Waveguide radiating elements having lower loss and capable of handling higher power. 7

A further object of the present invention is to provide waveguide radiating elements in a two-dimensional array which need not be wrapped around the waveguide thereby providing a smooth ground plane for better pattern and electrical performance.

In accordance with the present invention, a broadband slot radiating element is provided where-in no less than one driven slot radiator and no less than one parasitic or und-riven slot radiator is disposed in the narrow wall of increased-height rectangular waveguide. These slots may assume any conventional configuration and need not be restricted to the straight type. The driven and undriven slot radiators are grouped in close proximity to one another and comprise a single radiating element. That is, the mutual coupling between both the driven and the undriven slots is sufficiently great to eiliect operation of all the slots as a single broadband radiating element. The

driven slot radiators are disposed at an angle with respect to the transverse direction across the narrow wall of the increased-height rectangular waveguide. The parasitic slots, on the other hand, are disposed immediately adjacent the respective driven slots and extend transversely across the narrow wall of the waveguide. Increasedheight rectangular waveguide is employed to enable the slots to assume desired resonant lengths without necessit-ating the slot to wrap around to the broad wall. In the event the height of the waveguide exceedsone-half Wavelength as measured in the medium inside the waveguide, longi-tudinal conductive members are disposed transversely across the Waveguide on each side "of each group of slots constituting .a radiating element to attenuate propgation in a perpendicularly polarized mode. Lastly, each of the slots driven or parasitic which comprise a radiating element is cut to length such that the perimeter thereof corresponds to a different but adjacent resonant frequency. When one or more resonant lengths are employed, the complete radiating element constituting all the driven and parasitic slots responds in a manner similar to a coupled turned circuit thereby increasing the overall bandwidth of the radiating element.

The above-mentioned and other features and objects of this invention and the manner of obtaining them will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrates a perspective View of a length of waveguide of height less than one-half wavelength as measured within the medium inside the waveguide with fine driven and two parasitic slots of dumbbell configura- IOl'l;

FIGS. 2 and 3 illustrate partially cutaway perspective views of lengths of Waveguide of height greater than one-half wavelength as measured within the medium inside the waveguide and showing driven and parasitic slot radiating elementstogether with apparatus for attenuatingprop aga-tion in modes perpendicularly polarized to the dominant mode; and

FIG. 4 shows a plan view of a two-dimensional array of radiating elements in accordance with the present inverfiion composed of waveguide having common broad wa s.-

Referring now to FIG. 1 of the drawings, there is showna perspective view ofa length of waveguide 10- of Width W and height h In this embodiment of the invention, the height in is greater than what is referredto asthe standard height but less than one-half wavelength for the highest frequency adapted to be propagated along the waveguide 10 as measured within the medium inside the waveguide. In the usual case, the medium inside the waveguide 16 will have unity dielectric constant such as, for example, pressurized air, in which case the wavelength measurement will be the same as for free space. There are, however, instances where it is desired to fill the wave guide with oil or other dielectric material having a dielectric constant greater than unit whereby actual length of one-half wavelength will vary accordingly. 7

The waveguide 16 has opposite narrow walls 11, 12 and opposite broad walls 13, 14 as indicated in the drawing. In accordance with the present invention, a slot 16 is disposed in the narrow wall 11 of waveguide 10 at an acute angle 0 with the longitudinal axis thereof. The angle 0 is made less than so that the slot 16 couples to energy propagated in the dominant mode propagated along the waveguide 10. Further, the slot16 comprises a longitudinal portion 17 of predetermined width with two circular portions 18, 19 of a diameter of the order of twice this predetermined width thereby to increase the overall perimeter of the slot 16. Additional 3 p slots 21, 22 are disposed transversely across the narrow wall 11 on each side of the slot 16. The slot 21 has a straight portion 23 and circular portions 24, 25 at each extremity thereof, and the slot 22 has a straight portion 26 and circular portions 27, 28 at each extremity thereof similar to the dog-bone configuration of the slot 16. The overall length of the slots 16, 21, 22, however, are selected so that the perimeters correspond to selected spaced frequencies throughout the range of frequencies for which the radiating element is designed.

In operation, microwave energy is propagated in the dominant mode through the waveguide 16. In thedominant mode, boundary conditions within the waveguide result in currentflow that is transverse to the longitudinal axis of the waveguide 10 along the inner surface of the narrow wall 11. Only slots which interrupt this current flow are coupled to the energy propagated through the waveguide 10. Thus, only slot 16 is driven by the microwave energy propagated along the waveguide, the extent to which slot 16 is driven being determined by the acute ness of the angle That is, the smaller the angle 6 the higher the degree of coupling of the slot 16 to the energy within the waveguide 10. The slots 21, 22, on the other hand, being disposed transversely across the narrow wall 11 do not interrupt any current flow therein and, hence, are not coupled to energy being propagated by the waveguide 10. The slots 21, 22, however, are coupled to the slot 16 through mutual coupling which is enhanced at the resonant frequencies thereof, whereby the effective range of the combination of slots 16, 21 and 22 is substantially broader than that of the driven slot 16 operating alone. Lastly, in that the height I1 of waveguide is less than one-half wavelength as measured within the medium of the waveguide, no energy can be propagated therethrough in a mode that is perpendicularly polarized to the dominant mode.

Referring to FIG. 2, there is shown an alternate embodiment of the invention including a length of waveguide 30 having a width W2 and a height M, the height k in this embodiment being greater than one-half wavelength at the highest frequency of operation as measured within the medium inside the waveguide. The length of waveguide 30 has parallel narrow sides 31, 32 and parallel broad sides 33, 34. The narrow sides 31, 32 have a height 11 which is sufficiently large to enable the use of straight slots of sufficient length to provide resonances throughout the desired bandwidth. In particular, driven slots 35, 36 are disposed symmetrically about the center line of narrow wall 31 at angles 6 and 0 respectively, therewith. As

before, the angles 0 and'fi determine the degree of coupling of the respective slots 35, 36 to the energy propagated along the length of waveguide 30. Intermediate the slots 35, 36 there is disposed a slot 37 in the narrow wall 31 that is transverse to the longitudinal axis of the waveguide 30. The slots 35, 36, 37 are all of uniform width and are varying lengths to effect resonances throughout a desired bandwidth of frequencies. The extremities of the slots 35, 36, 37 may be rounded as shown in the drawing for convenience of fabrication. In that slot 37 is parasitic, it is desirable that it have a length intermediate the lengthsof the driven slots and 36 to achieve a more uniform response throughout the desired range of operation.

In addition to the foregoing, conductive rods 38, 39 and 4t 41 are disposed transversely across the width W2 of the waveguide 30 on opposite sides of the group of slots 35, 36, 37, respectively. Therods 38, 39 and 4t), 41 are connected to the narrow walls 31, 32 along the respective center portions thereof with a spacing that is not critical. Alternatively, a single rod may be employed on either side of the group of slots35, 36, 37 if desired.

In order to pre- 4 vent the propagationof waves in this mode, the conductive rods 38, 39, 4t), 41 are disposed transversely across the width of waveguide 30 thereby to prevent the establishment of an electric field that is perpendicular to the electric field of the dominant mode. The slots 35, 36, 37 function in the samemanner as before, the slots 35, 36 being coupleddirectly to energy'propagated along the length of waveguide 30 and the slot 37 being parasitically coupled thereto through mutual coupling to the slots 35, 36 to extend the overall frequencyrange of operation. The angles 0 and 0 rnay be normally selected to provide substantially equal coupling of the slots 35, 36 .to energy within the waveguide 30 at the center frequency.

Referring to FIG. 3, there is shown an embodiment of the invention wherein the waveguide-30 has one driven slot 42 disposed in the narrow side 31 at an angle .6 with the center linethereof and with parasitic slots 43, 44 on both sides thereof. As before, the perimeters of the slots 42, 43, 44 are of different lengths'to establish resonances throughout a desiredrange of operation. In addition, conductive septums 45, 46 are disposed transversely cross the waveguide 30 between the narrow walls 31, 32 on each side of the group of slots'42, 43, 44. The septums 45, 46 are attached to the narrow walls 31, 32 along the center lines thereof. The width of the septums 45, 46 is not critical and is generally chosen to achieve the desired attenuation of the perpendicularly polarized mode; The operation of the device of FIG. 3 is essentially the same as that of FIG. 2 with the exception that only driven slot 42 in this embodiment couples to energy propagated through the waveguide 30. The slots 43, 44 are coupled to the slot 42 and, hence, provide resonances at di ferent frequencies thereby increasing the overall range of operation.

Referring to FIG. 4, there is shown a two-dimensional array 50 employing radiating elementsin accordance with the present invention. In particular, the two-dimensional array 50 includes equal length waveguides 51, 52, 53, 54, 55, 56, 57, 58, 59 and 60 disposed coextensively with common broad walls between the waveguides 51, 52; 52, 53; 53, 54; 54, 55; 55, 56; 56, 57; 57, 58; 58, 59; and 59, 60. Each of the waveguides 59, 60 includes a plurality of radiating elements 61 of a predetermined phase and radiating elements 62 of opposite phase interposed therebetween. The phase of a radiating element may be reversed by slanting the slots at the supplement of the angle 6. In addition, the waveguides 51, 60 are coupled through a microwave feed network 63 and a waveguide 64 to atransmitter-receiver system 65, all of which may be of conventional type. Lastly, the waveguides 51-60 are terminated by non-reflecting terminations 66. In that the intermediate broad walls of the waveguides 51-60 are common, the waveguides 51-60 may be pressurized by additional reinforcing for these portions of the antenna. The overall operation of the two-dimensional array 50 is conventional.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

What is claimed is: V

1. A radiating element comprising a rectangular waveguide having first and second parallel narrow walls and first and second parallel broad walls for propagating electromagnetic energy therethrough within a predetermined band of frequencies; a first slot of a first predetermined perimeter disposed only in said first narrow wall at an acute angle with the center line thereof thereby to couple to said rectangular waveguide, said first predetermined perimeter corresponding to a resonance at a first selected frequency within said predetermined band of frequencies; and a second slot of a second perimeter different from said first predetermined perimeter having mutual coupling to said first slot and disposed only in said first narrow wall transverse to the center line thereof, said second perimeter corresponding to a resonance at a second selected frequency within said predetermined band of frequencies.

2. The radiating element as defined in claim 1 wherein the width of said first and second narrow walls is greater than one-half wavelength at the highest frequency of said predetermined band of frequencies as measured in the medium inside said waveguide and said radiating element additionally includes a longitudinally conductive member disposed transversely across said waveguide from said first narrow wall to a corresponding point on said second narrow wall immediately adjacent to said first and second slots.

3. A radiating element comprising a rectangular waveguide having broad and narrow Walls for propagating electromagnetic energy within a predetermined band of fre quencies therethrough, said narrow walls being less than one-half wavelength at the highest frequency of said predetermined band of frequencies as measured in the medium inside said waveguide; a first slot of a first predetermined perimeter disposed only in one of said narrow walls at an acute angle with the center line thereof thereby to couple to said waveguide, said first predetermined perimeter being of a length to correspond to resonance at a first selected frequency within said predetermined band of frequencies; and a second slot of a second perimeter different from said first predetermined perimeter having mutual coupling to said first slot and disposed only in said one narrow wall transverse to the center line thereof, said second perimeter corresponding to resonance at a second selected frequency within said predetermined band of frequencies.

4. A radiating element comprising a rectangular waveguide having first and second parallel narrow walls and first and second parallel broad walls for propagating electromagnetic energy therethrough within a predetermined band of frequencies, the width of said first and second narrow walls being greater than one-half wavelength at the highest frequency of said predetermined band of frequencies as measured in the medium inside said waveguide; a first slot of a first predetermined perimeter disposed only in said first narrow wall transversely thereacross, said first predetermined perimeter corresponding to resonance at a first selected frequency within said predetermined band of frequencies; and second and third slots having second and third perimeters that are smaller and larger than said first predetermined perimeter, respectively, disposed on opposite sides of said first slot at respective acute angles with the center line of said first narrow wall, said second and third perimeters corresponding to resonances at second and third selected frequencies that are above and below, respectively, said first selected frequency and within said predetermined band of frequencies; and a longitudinal conductive member extending "from said first narrow wall to a corresponding position on said second narrow wall transversely across and in the center portion of said waveguide on no less than one side of said first, second and third slots.

5. The radiating element as defined in claim 4 wherein said longitudinal conductive member constitutes a conductive rod attached to said first and second narrow walls at the respective center lines thereof.

6. The radiating element as defined in claim 4 wherein said longitudinal conductive member constitutes a septum 6 of conductive material with the fiat surfaces thereof dis posed parallel to said first and second broad sides.

7. A radiating element comprising a rectangular waveguide having first and second parallel narrow walls and first and second parallel broad Walls for propagating electromagnetic energy therethrough within a predetermined band of frequencies, the width of said first and second narrow walls being greater than one-half wavelength at the highest frequency of said predetermined band of frequencies as measured in the medium inside said wave guide; first and second slots of first and second different perimeters, respectively, disposed only in said first narrow wall transversely thereacross, said first and second perimeters corresponding to resonances at first and second selected frequencies within said predetermined band of frequencies; and a third slot having a third perimeter that is intermediate said first and second perimeters disposed at an acute angle with the center line of said first narrow wall in between and mutually coupled to said first and second slots, said third perimeter corresponding to resonances at a third selected frequency that is intermediate said first and second selected frequencies; and a longitudinal conductive member extending from said first narrow wall to a corresponding position on said second narrow wall transversely across said waveguide within the center portion thereof .on no less than one side of said first, second and third slots.

8. A two-dimensional array comprising a plurality of equal lengths of rectangular waveguide, the broad sides of said respective lengths of rectangular waveguide being coextensive with the broad sides of adjacent lengths of rectangular waveguide; a first plurality of radiating elements disposed at uniform intervals along each length of rectangular waveguide in the respective narrow walls on a common side thereof, each of said radiating elements including no less than one transverse slot and no less than one additional slot mutually coupled to said transverse slot and disposed at respective acute angles with the longitudinal axis of said Waveguide; a second plurality of radiating elements disposed intermediate each of said radiating elements of said first plurality, each radiating element of said second plurality thereof including a transverse slot and an additional slot disposed at respective angles relative to the longitudinal axis of said waveguides that are supplementary to said respective acute angles of said additional slots of said first plurality of radiating elements; means for providing a non-reflecting termination for each of said waveguides at one extremity there-' of; and means including a transmitter and receiver system coupled to the respective remaining extremities of said waveguides for generating a directive beam pattern from said two-dimensional array.

References Cited by the Examiner UNITED STATES PATENTS 2,573,746 11/51 Watson 343771 2,840,818 6/58 Reed et a1 343770 2,908,905 10/59 Saltzman 343771 2,932,823 4/60 Beck 343771 2,981,994 4/ 61 Washburne 343768 3,004,259 10/ 61 Shanks 343768 3,005,984 10/61 Winter 343768 3,031,665 4/ 62 Marie 343--770 3,106,713 10/63 Murata et a1. 343770 HERMAN KARL SAALBACH, Primary Examiner. 

1. A RADIATING ELEMENT COMPRISING A RECTANGULAR WAVEGUIDE HAVING FIRST AND SECOND PARALLEL NARROW WALLS AND FIRST AND SECOND PARALLEL BROAD WALLS FOR PROPAGATING ELECTROMAGNETIC ENERGY THERETHROUGH WITHIN A PREDETERMINED BAND OF FREQUENCIES; A FIRST SLOT OF A FIRST PREDETERMINED PERIMETER DISPOSED ONLY IN SAID FIRST NARROW WALL AT AN ACUTE ANGLE WITH THE CENTER LINE THEREOF THEREBY TO COUPLE TO SAID RECTANGULAR WAVEGUIDE, SAID FIRST PREDETERMINED PERIMETER CORRESPONDING TO A RESONANCE AT A FIRST SELECTED FREQUENCY WITHIN SAID PREDETERMINED BAND OF FREQUENCIES; AND A SECOND SLOT OF A SECOND PERIMETER DIFFERENT FROM SAID FIRST PREDETERMINED PERIMETER HAVING MUTUAL COUPLING TO SAID FIRST SLOT AND DISPOSED ONLY IN SAID FIRST NARROW WALL TRANSVERSE TO THE CENTER LINE THEREOF, SAID SECOND PERIMETER CORRESPONDING TO A RESONANCE AT A SECOND SELECTED FREQUENCY WITHIN SAID PREDETERMINED BAND OF FREQUENCIES. 